Surgical instrument for grinding the cotyloid cavity

ABSTRACT

A surgical instrument for grinding the cotyloid cavity includes an instrument head and a drive shaft. In order to offer easier access during a minimally invasive operation, the drive shaft, which can include an optionally provided shank, is located at an angle with respect to the rotation axis of the instrument head. In order to facilitate the alignment of the instrument head and the exertion of the advancing force, a handle can be provided that is located in the direction of the rotational axis of the instrument head but is connected to the instrument head or to the shank at a location outside of the rotational axis.

REFERENCE TO RELATED APPLICATIONS

This is a national stage application under 35 USC 371 of InternationalApplication No. PCT/EP03/00191, filed Jan. 10, 2003, which claimspriority under 35 USC 119 from prior International Application No.PCT/EP02/00223, filed Jan. 11, 2002, and German patent application No.10221614, filed May 15, 2002.

FIELD AND BACKGROUND OF THE INVENTION

To insert a prosthetic socket into the natural acetabulum, the latterhas to be ground out. To do so, it has hitherto been necessary to havean open access in the direction of the acetabulum axis in order to beable to apply a grinding instrument with a shank extending in thegrinder axis. This applies even in minimally invasive operatingtechniques (WO 01/91648, U.S. Pat. No. 2,785,673) when a correspondingbore is created through the proximal part of the femur. This iscomplicated and weakens the femur. For cases where accessibility ispoor, grinding instruments are known (U.S. Pat. Nos. 5,176,711;4,808,185; 6,364,910, not published) in which the drive shaft is locatedat an angle with respect to the rotation axis of the instrument head.This makes it difficult to exactly align the grinding instrument withthe acetabulum axis and to exert the axial machining force. This appliesin particular to minimally invasive access when the operating field isdifficult to see or cannot be seen.

SUMMARY OF THE INVENTION

According to the invention, the solution to this difficulty is achievedby a surgical instrument having the features of the invention as broadlydisclosed hereinafter.

The instrument has an instrument head equipped with the grinder. Theinstrument head is connected to a holder by means of which it is held inthe desired working position. For driving the grinder, a drive shaft isprovided which connects it to a drive device and is located at an anglewith respect to the rotation axis of the instrument head. This makes itpossible to bring the instrument toward the acetabulum from a directionwhich does not coincide with the direction in which the acetabulumopens. It is thus suitable for a minimally invasive access to theacetabulum, for example for an anterolateral or posterolateral approach.

According to the invention, a support part is provided which acts on theinstrument head in the direction of the rotation axis and makes itpossible to apply a machining force in this direction and/or to alignthe instrument. This support part can be formed by a handle which isconnected to the instrument head via a bow located outside of therotation axis of the instrument head. The bow can also be connected to apin belonging to the holder of the instrument. The bow allows theinstrument head to be brought toward the acetabulum from the side,through what can be a narrow surgical opening, and then to exert anadvancing force still in the direction of the working axis. In this way,the operating surgeon also obtains an exact idea of how the operatingaxis of the instrument lies, which makes it easier for him to align theinstrument.

In another embodiment of the invention, the instrument head can also besupported on the femur which, particularly in minimally invasiveoperating techniques, is sufficiently connected to the hip bone byligaments and muscles and is therefore able to take up the machiningforces. Moreover, according to the invention, the femoral neck can beused for aligning the instrument. This is based on the concept that thedirection of the femoral neck in many cases coincides with the desireddirection of the grinder. At any rate, this is true if the ligamentapparatus is sufficiently retained and the operating surgeon takes carethat the leg is in a natural position relative to the acetabulum. Forthis support on the femur, the holder of the instrument head can have afemur attachment part arranged on that side of the instrument headfacing away from the grinder. Depending on the desired purposes, thisfemur attachment part can be designed with a supporting function only,or with a direction-defining function only, or with both. Furtherdetails of this are discussed below.

The holder of the instrument head expediently comprises a shank which,like the drive shaft, is located at an angle with respect to therotation axis of the instrument head. The angle of the shank or driveshaft with respect to the rotation axis of the instrument head isexpediently between 90 and 135°, measured on the side directed towardthe grinder. As in the known instruments mentioned, this angle can beinvariable. However, it can also be adjustable and if appropriate fixedin a desired position or be freely variable so that the physician canoptimally adapt the direction of the handle to the particularcircumstances during grinding. The drive shaft can be connected to theshank. However, this is not absolutely necessary. It is preferablyflexible if no shank is provided or if this is separate from the driveshaft.

In general, the shank is connected fixedly to the instrument head.However, it may sometimes be advantageous if it is easily detachable,and, from case to case, can be connected to the instrument head andreleased from the latter during surgery. It is then possible to providedifferently designed or oriented shanks in order to satisfy differentaims of the operating surgeon and different anatomical conditions. Thisis true in particular when the bow mentioned above is connected to theshank. The shank is not connected to the drive shaft in the detachabledesign.

If the femur is used to support the instrument head and/or to determineits direction, this can be done using an attachment part which enclosesthe femoral neck on the outside along a certain length. In another,preferred embodiment of the invention, the attachment part is formed bya journal which extends in the direction of the rotation axis of thegrinder and cooperates with a bore that the operating surgeon has madebeforehand from the resection surface into the femoral neck. Thisjournal can be connected fixedly to a housing part of the grinder. Itcan also be formed by a continuation of the grinder shaft and turn withthe grinder. In this case, it is expedient if a bushing is providedwhich can be fitted into the bore in the femoral neck and receives thejournal. The femur attachment part can also be provided with meanssecuring the instrument head against turning.

The femur attachment part can form the only holder for the instrumenthead. However, it is often expedient to additionally provide theaforementioned shank to ensure that the alignment of the instrument andthe advancing movement can be controlled and influenced from outside. Inthis case, the abovementioned detachable design may be expedient. It mayfurther be expedient to design the femur attachment part and the shankin such a way that they can be used alternately. For example, thejournal facing the femur on the instrument head can be used alternatelyfor connection to the shank instead of to the femur. If so desired, theconnection between the instrument head and the shank or femur can be ofsuch design that the grinding torque is taken up via the shank or femur.

In the embodiment in which the femur is used as a bearing for generatingthe advancing force, said advancing force can be generated or increasedby the femur attachment part comprising a means for support on the femurand by an extension mechanism being arranged between this support meansand the instrument head. This extension mechanism presses the instrumenthead away from the support means when a corresponding advancing force isexerted on it. For this purpose, it can be connected fixedly orreleasably to an advancer rod. The latter should be located at an anglewith respect to the rotation axis of the instrument head, like the driveshaft and/or the shank, and specifically to the same side. The extensionmechanism forms a gear in its most general sense, which converts themovement set by the advancer rod into an extension of the distancebetween the instrument head and the support means. A wide variety ofgear configurations are readily available to the engineer for thispurpose. For example, a lever mechanism can be chosen which converts apivoting movement of the advancer rod, about a pivot axis lyingtransverse to the rotation axis of the instrument head, into anextension movement of the extension mechanism. The extension mechanismwith the advancer rod can in this case be designed as spreader forceps;in this case the advancer rod is formed by a pair of forceps levers. Theextension mechanism can also be formed by a rotary gear; in this casethe advancer rod is turned in order, for example, to act, via a pinionprovided at its end, on a toothed rack which effects the extension ofthe mechanism.

So that the instrument head can be introduced from the side through anarrow surgical opening, its size should be kept as small as possible inthe direction of the grinder axis. A measure of this size is thedistance between the intersection point of the rotation axis of theinstrument head with the axis of the shank or drive shaft, on the onehand, and the center point of the grinder, on the other hand. Thisdistance should be as small as possible. It should not be greater thanthe grinder diameter and preferably not greater than half the grinderdiameter. The external size of the instrument head, measured in thedirection of the grinder axis, is expediently not greater than 8 cm,preferably not greater than 6 cm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference to thedrawing which shows advantageous illustrative embodiments.

FIG. 1 shows a longitudinal section through the instrument,

FIG. 2 shows a diagrammatic view of an alternative embodiment of theinstrument,

FIG. 3 shows a third embodiment of the equipment in use,

FIG. 4 shows a fourth embodiment, and

FIG. 5 shows a fifth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The housing parts 1, 2 of the instrument head 3 shown in FIG. 1 areconnected fixedly to a shank 4 which forms a handle 15 and contains adrive shaft 5 whose free end 6 can be connected in a known manner to adrive motor or to a grip for manual operation. Inside the housing 1, 2,the drive shaft 5 carries a toothed pinion 7.

Also in the housing 1, 2 of the instrument head 3, a grinder shaft 8 isalso mounted so as to rotate transverse to the drive shaft 5. The anglebetween the two shafts is expediently between 90 and 135° (110° in thecase shown). The grinder shaft carries a bevel gear 9 whose teeth engagewith those of the pinion 7. The grinder shaft 8 can in this way bedriven in rotation by the drive shaft 5. It will be appreciated thatthis is just one example of the drive connection between the two shafts.Other gear types can be used, for example a worm gear. The gear itself,or a cardan part connected to it, can be configured with angle tolerancein order to permit adjustment of the angle between the shafts 5 and 8. Afixing means can be provided which allows the instrument to be locked inthe chosen angle setting. Instead of this, it is also possible toprovide free angle movement.

A semispherical grinder tool 10, known per se, and referred to in thisdescription simply as a grinder, is fitted onto the end of the grindershaft 8 in a manner known per se and so as to be exchangeable. To keepthe size of the instrument head to a minimum, the grinder is locatedclose up to the housing 1, 2 of the instrument head.

The distance of the center point 22 of the grinder or of the centerpoint of its rear face from the intersection point 21 of the axes of theshafts 5 and 8 is smaller than the radius of the grinder, preferablysmaller than a quarter of the grinder diameter. If the grinder is notsemispherical in shape, said diameter is replaced by the greatestdiameter.

Extending from the side of the instrument head 3 facing away from thegrinder 10, there is a journal 11 which is connected fixedly, ifappropriate in one piece, to the grinder shaft 8 and has a commonrotation axis 12 with the latter. A sleeve 13 with terminal flange 14 isfitted onto the journal 11 with a sliding fit. On its side facing towardthe bone, the flange has teeth or needles 18 which penetrate into thebone in order to prohibit rotation of the sleeve 13.

The instrument is used in the following way. After the head of the hiphas been removed, a blind hole is formed in the femoral neck, startingfrom its resection surface and on the same axis, and the sleeve 13 isinserted into this blind hole. The instrument is introduced in such away that the journal 11 is fitted into the sleeve 13 sitting in the borein the femur. The leg is positioned normally so that the femoral neckpoints to the acetabulum and the grinder lies in place of the naturalhead of the hip in or on the acetabulum. The grinder 10 is pressed intothe acetabulum by the ligaments holding the proximal femur and is at thesame time aligned naturally. The acetabulum can now be ground outcompletely, with or without slight orientation assistance from theoperating surgeon. Thereafter, the operation is continued in the knownmanner.

While the illustrative embodiment according to FIG. 1 makes do with ahandle shank protruding transversely from the instrument head 3, aninstrument is indicated diagrammatically in FIG. 2 whose handle 15′ isarranged approximately in the axis 12 of the grinder 10. The shank 4′ ofthe instrument protrudes approximately perpendicularly from theinstrument head 3′ and carries a drive motor 16 at its end. The end ofthe shank 4′ is connected rigidly to the handle 15′ by means of a bow17. The position of the handle provides the operating surgeon with aprecise indicator of the position of the grinder axis 12 and allows himnot only to align the grinder in the desired axis direction but also tocontrol the force with which the grinder is pressed into the acetabulum.The handle can be designed flat in the dot-and-dash line to make iteasier to orient the force with the hand or the body of the operatingsurgeon.

The instrument according to FIG. 3 differs from the one shown in FIG. 1in that it does not have a shank, and the drive shaft 5″ is designed asa flexible shaft. As has been explained with reference to FIG. 1, thealignment of the instrument is effected by the sleeve 13 inserted intothe bone 19 and by the journal 11 located therein. The advancing forceneeded for grinding is also transmitted from the bone 19 to theinstrument. By virtue of the flexibility of the drive shaft 5′, thealignment of the instrument defined by the femur is not adverselyaffected by inadvertent movements of the operating surgeon. However, theshaft 2′ is stiff enough to be able to transmit the grinding torque. Arotationally fixed connection can also be provided between theinstrument head 3 and the flange of the sleeve 13, the flange in turnbeing connected in a rotationally fixed manner to the bone by teeth orneedles 18 (FIG. 1) in order to bear on the latter in respect of thegrinding torque.

FIG. 4 shows a variant of the instrument, for whose descriptionreference may be made to FIG. 1. The end 25 of a lever 26 is interposedbetween the housing 1, 2 and the flange 14. This end is designed like afork so that, if desired, it can be pushed in at a later stage betweenthe housing 1, 2 and the flange 14. It is angled slightly with respectto the long end 26 of the lever. It is first pushed in parallel betweenthe rear face of the housing 1, 2 and the flange 14. The long end 26 ofthe lever is then located at a certain angle distance from the shank 4.If an advancing force is to be generated in order to press the grinder10 into the acetabulum, the long end 26 of the lever is pressed towardthe shank 4 in the direction of the arrow. The operating surgeon canexecute this movement easily in the manner of actuating a forceps. Indoing so, the bend point 27 of the lever bears on the rear face of thehousing 1, 2 and forms the pivot point for its subsequent pivotingmovement. The tip 28 bears on the flange 14 and presses it away from thehousing 1, 2 as the pivoting movement continues. The lever end 25 thusforms an extension mechanism together with the rear face of the housing1, 2 and the flange 14. The long end 26 of the lever forms an advancerrod, upon whose movement the extension mechanism is extended in order toincrease the distance of the grinder 10 from the bone 19 on which theflange 14 of the sleeve 13 bears, and thus to press the grinder 11 intothe acetabulum.

In the fifth embodiment according to FIG. 5, a grinder 10 is connectedto the instrument head 3 in the manner explained above. A shank 4 isconnected to the instrument head 3 at right angles to the grinder axis,said shank 4 containing a drive shaft to whose free end 6 a drive motorcan be coupled. A journal 31 is rigidly connected to the instrument head3. It can be inserted into the bore of a sleeve 13 which for its part isfitted into the femoral neck remaining after resection of the head ofthe hip, as has been described above. The journal 31 then serves toorient the instrument head 3 and the grinder 10 in the direction of theneck of the femur. In this way too, the necessary press-on force can betransmitted to the grinder 10.

In order to be able to transmit additional force to the instrument head3 and if appropriate also to be able to align the instrument, a bow 33with handle 34 is provided. The handle lies in the same axis as therotation axis of the grinder 10 and the axis of the journal 31. The bowis made stiff enough to be able to transmit the press-on force andguiding force from the handle 34 to the instrument head 3. Couplingmembers 32, 35 matching each other are provided on the instrument head 3and at the end of the bow 33 remote from the handle, these couplingmembers 32, 35 preferably being designed in such a way that they can beclosed or released quickly and simply, as may be necessary during theoperation. For such couplings, a large number of technical possibilitiesare available. In the example shown, they are configured as follows. Onthe bow, a coupling fork 35 is provided which has a fork openingdelimited by profiled fork flanks 36 on both sides. The coupling element32 on the instrument head 3 is designed to match the fork opening andhas a profiled contour complementing that of the flanks 36. For example,the flanks 36 can have a central rib corresponding to a groove on thecoupling element 32. The coupling element 32 is round, so that thecoupling fork 35 can be fitted on from any direction. This constructiongives the operating surgeon freedom in respect of the direction fromwhich he wishes to fit the bow onto the instrument. If this is notdesired, the coupling element 32 can, for example, be designed as asquare with parallel profiled sides which fit into the coupling openingof the fork 35, but define a coupling direction with the latter.

To ensure that the coupling fork 35 cannot inadvertently slip from thecoupling element 32 on the instrument, a securing hook 37 is providedwhich is pivotable about an axis 38 so that it can be moved from therelease position, shown in FIG. 5, to the securing position in which itcloses around the journal 31 when the coupling element 32 is located inthe fork opening, and vice versa. The securing hook can be connected toa locking device which prohibits undesired withdrawal from the securingposition.

1. A surgical instrument for grinding the cotyloid cavity, comprising an instrument head having a rotation axis and with grinder thereon, a holder for holding the instrument head in a working position, a drive device, a drive shaft which connects the grinder to the drive device and is located at an angle with respect to the rotation axis of the instrument head, and a support part arranged in the direction of the rotation axis and acting on the instrument head, wherein the support part comprises a femur attachment part arranged on a side of the instrument head facing away from the grinder, the femur attachment part determines a grinding direction, and the femur attachment part comprises a journal extending in the direction of the rotation axis of the instrument head.
 2. The instrument as claimed in claim 1, wherein the holder comprises a shank located at an angle with respect to the rotation axis of the instrument head.
 3. The instrument as claimed in claim 2, wherein the drive shaft is arranged in or on the shank.
 4. The instrument as claimed in one of claims 1 through 3, wherein the journal is formed by a grinder shaft.
 5. The instrument as claimed in claim 4, further comprising a bushing for the journal formed by the grinder shaft which can be inserted into a bore in the femur.
 6. The instrument as claimed in claim 5, wherein the angle between the rotation axis of the instrument head and the drive shaft or the shank is adjustable.
 7. The instrument as claimed in claim 5, further comprising a separate shank detachably connected to the instrument head.
 8. The instrument as claimed in claim 5, further comprising a grinder advancer device for advancing the instrument head with support on the femur.
 9. The instrument as claimed in claim 8, wherein the femur attachment part comprises a support on the femur, and wherein the instrument further comprises an extension mechanism arranged between the support and the instrument head.
 10. The instrument as claimed in claim 5, wherein the instrument has an outer dimension, measured in the direction of the grinder axis without including parts optionally to be accommodated in the femur and including the grinder, of not greater than 8 cm.
 11. The instrument as claimed in claim 4, wherein the angle between the rotation axis of the instrument head and the drive shaft or the shank is adjustable.
 12. The instrument as claimed in one of claims 1 through 3, wherein the angle between the rotation axis of the instrument head and the drive shaft or the shank is adjustable.
 13. The instrument as claimed in one of claims 1 through 3, further comprising a separate shank detachably connected to the instrument head.
 14. The instrument as claimed in one of claims 1 through 3, further comprising a grinder advancer device for advancing the instrument head with support on the femur.
 15. The instrument as claimed in claim 14, wherein the femur attachment part comprises a support on the femur, and wherein the instrument further comprises an extension mechanism arranged between the support and the instrument head.
 16. The instrument as claimed in one of claims 1 through 3, wherein the distance between the intersection point of the rotation axis of the instrument head and the axis of the shank or drive shaft, on the one hand, and the center point of the grinder, on the other hand, is not greater than the grinder diameter.
 17. The instrument as claimed in claim 16, wherein the distance is not greater than half the grinder diameter.
 18. The instrument as claimed in one of claims 1 through 3, wherein the instrument has an outer dimension, measured in the direction of the grinder axis without including parts optionally to be accommodated in the femur and including the grinder, of not greater than 8 cm. 